Electronic component built-in substrate and method of manufacturing electronic component built-in substrate

1. A method of manufacturing an electronic component built-in substrate, comprising the steps of: mounting an electronic component at a predetermined portion of a first wiring board; performing wire-bonding to electrically connect a bonding pad formed on the first wiring board to an electrode of the electronic component by a bonding wire; coating at least a connection portion between the electrode of the electronic component and the bonding wire with a protection material; arranging the first wiring board and a second wiring board so that one side surface of the second wiring board formed separately from the first wiring board faces one surface of the first wiring board with the electronic component disposed between the first wiring board and the second wiring board, and electrically connecting the first wiring board and the second wiring board to each other by reflowing a solder ball; reflowing the solder ball to clean a portion between the first wiring board and the second wiring board; and sealing a portion between the first wiring board and the second wiring board with a sealing material that is in addition to and distinct from the protection material by casting the sealing material with a capillary action such that the sealing material covers and contacts the one side surface of the second wiring board and the one surface of the first wiring board and fills the portion between the first wiring board and the second wiring board.

2. The method of manufacturing an electronic component built-in substrate according to claim 1 , wherein in the step of coating the connection portion between the electrode of the electronic component and the bonding wire with the protection material, the connection portion between the electrode of the electronic component and the bonding wire is coated with the protection material in a state in which a top-most part of a wire loop formed of the bonding wire is exposed.

3. The method of manufacturing an electronic component built-in substrate according to claim 1 , wherein the sealing material completely fills the portion between the first wiring board and the second wiring board.

4. The method of manufacturing an electronic component built-in substrate according to claim 1 , wherein the sealing material is formed of resin.

5. The method of manufacturing an electronic component built-in substrate according to claim 1 , wherein the solder ball is a core-contained solder ball formed by coating an outer surface of a spherical body, which is formed of an electrical conductor as a core, with solder.

6. The method of manufacturing an electronic component built-in substrate according to claim 1 , wherein the electronic component comprises a first electronic component and a second electronic component, and wherein the first electronic component is disposed on one of the wiring boards and the second electronic component is disposed on the first electronic component.

7. An electronic component built-in substrate, comprising: a first wiring board comprising a first pad and a bonding pad thereon; a second wiring board comprising a second pad thereon and facing the first wiring board with a gap interposed therebetween such that the first pad and the second pad face each other; a solder ball comprising a core and a solder covering at least a portion of the core, the solder ball being provided between the first wiring board and the second wiring board so as to electrically connect the first wiring board and the second wiring board, wherein portions of the core exposed from the solder directly contact the first pad and the second pad; an electronic component comprising an electrode thereon and mounted on the first wiring board such that the electrode is electrically connected to the bonding pad through a bonding wire; a sealing resin that seals the gap between the first wiring board and the second wiring board such that the sealing resin covers and contacts facing surfaces of the first and second wiring boards and fills the gap, wherein at least a connection portion between the electrode and the bonding wire is coated with a protection material which is in addition to and distinct from the sealing resin, wherein the minimum distance of the gap between the first wiring board and the second wiring board is substantially equal to the diameter of core of the solder ball, wherein the bonding wire has a wire loop portion, a top of the wire loop portion is exposed from the protection material, and wherein the minimum distance between the top of the wire loop portion and the facing surface of the first wiring board is smaller than the diameter of the core of the solder ball.

8. The electronic component built-in substrate according to claim 7 , wherein the resin completely fills the gap.

9. The electronic component built-in substrate according to claim 7 , wherein the electronic component comprises a first electronic component and a second electronic component, and wherein the first electronic component is disposed on one of the wiring boards and the second electronic component is disposed on the first electronic component.

10. The substrate of claim 7 , wherein the electrode comprises a plurality of electrodes, the bonding pad comprises a plurality of boding pads, and the bonding wire comprises a plurality of bonding wires, the plurality of electrodes are arranged in a line along a side of the electronic component, and the plurality of boding pads are arranged in a line, and each of the plurality of electrodes is electrically connected to a corresponding one of the plurality of the bonding pads through a corresponding one of the plurality of bonding wires.